1. Field of the Invention
The present invention relates to a layer member forming method which is suitable for use in the fabrication of various electronic devices of the type having an insulating, protecting, conductive, semiconductor or like layer member formed on a substrate member.
2. Description of the Prior Art
Heretofore there has proposed a method for forming such a layer member on a substrate member through use of a photo CVD or plasma CVD process.
According to the method utilizing the photo CVD technique, the substrate is placed in a reaction chamber provided with a light transparent window and a reactive gas mixture, which contains at least a gas of a material for the formation of the layer member desired to obtain, is introduced into the reaction chamber. Then light is introduced into the reaction chamber through the light transparent window thereof by which the reactive gas mixture introduced thereinto is excited for vapor-phase decomposition and the material for the layer is deposited on the substrate member.
With the method utilizing the plasma CVD technique, the substrate is placed in a reaction chamber and a reactive gas mixture, which contains a gas of a material for the formation of the layer, is introduced into the reaction chamber. In the reaction chamber the reactive gas mixture is excited into a plasma by glow discharge or electron cyclotron resonance for vapor-phase decomposition by high frequency electric power so that the material for the layer is deposited on the substrate.
With the photo CVD process, since the material gas resulting from the vapor-phase decomposition of the photo-excited reactive gas is not accelerated, it is possible to form the layer on the substrate with substantially no damage inflicted on the substrate surface. On this account the layer can easily be formed without containing the material forming the substrate surface or without introducing into the substrate surface the material forming the layer, without developing any undesirable interface level between the layer and the substrate and without applying any internal stress to the layer and the substrate. Furthermore, since the photo-excited material gas has a characteristic to spread on the surface of the substrate member, the layer can be deposited in close contact with the substrate even if the substrate surface is uneven.
Accordingly, the use of the photo CVD technique permits easy formation of the layer of desired characteristics, without causing any damages to the substrate surface, even if the substrate has an uneven surface.
With the photo CVD process, however, since the photo-excited material gas is not accelerated toward the substrate, the deposition rate of the layer is lower than in the case of employing the plasma CVD technique. Therefore, the photo CVD process takes much time for forming the layer as compared with the plasma CVD process. Furthermore, the material for the layer is deposited as well on the light transparent window during the formation of the layer, causing a decrease in the light transmittivity of the window as the deposition proceeds. Therefore, the layer cannot be formed to a large thickness. For instance, in the case of forming a silicon nitride layer, it is difficult, in practice, to deposit the layer to a thickness greater than 1000 A. Moreover, difficulties are encountered in forming a silicon layer to a thickness greater than 200 A, a silicon oxide (SiO2), or aluminum nitride (AlN) layer to a thickness greater than 3000 A, a silicon carbide (SixC1xe2x88x92x, where 0 less than x less than 1) layer to a thickness greater than 500 A and a germanium silicide (SixGe1xe2x88x92x, where 0 less than x less than 1) or metal silicide (SiMx, where M is metal such as Mo, W, In, Cr, Sn Ga or the like and 0 less than Xxe2x89xa64) layer to a thickness greater than 100 to 200 A.
With the plasma CVD process, since the material gas resulting from the vapor decomposition of the reactive gas excited by electric power can be accelerated toward the substrate, the deposition rate of the layer is higher than in the case of using the photo CVD process. Therefore, the layer can be formed on the substrate in a shorter time than is needed by the photo CVD technique. Furthermore, even if the material for the layer is deposited on the interior surface of the reaction chamber as well as on the substrate, no limitations are imposed on the excitation of the reactive gas by electric power. Consequently, the layer can easily be formed to a desired thickness on the substrate.
With the plasma CVD technique, however, since the material gas excited by electric power is accelerated by an electric field, it is difficult to deposit the layer on the substrate without causing damage to its surface. On account of this, the layer contains the material forming the substrate surface, or the substrate surface contains th material forming the layer. Moreover, an interface level is set up between the layer and the substrate and internal stresses are applied to the layer and the substrate.
Besides, in the case of employing the plasma CVD technique, since the excited material gas is accelerated by an electric field and its free running in the reaction chamber is limited, there is the possibility that when the substrate surface is uneven, the layer cannot be formed in close contact therewith, that is, the layer cannot be deposited with desired characteristics.
It is therefore an object of the present invention to provide a novel layer member forming method which is free from the abovesaid defects of the prior art.
The layer member forming method of the present invention comprises the steps of depositing a layer of a desired material on a substrate by the photo CVD technique and depositing on the first layer a second layer of a material identical with or different from that of first layer by the plasma CVD technique, thereby forming a layer member composed of at least the first and second layers.
According to such a method of the present invention, since the first layer is deposited by the photo CVD technique on the substrate, even if the substrate surface is uneven, the first layer can be deposited in close contact with the substrate surface and with substantially no damage thereon. Accordingly, the first layer does not substantially contain the material forming the substrate surface, or the substrate surface does not substantially contain the material forming the first layer. Further, the deposition of the first layer is not accompanied by provision of an undesirable interface level between the first layer and the substrate and the application of internal stresses to the first layer and the substrate. In addition, since the second layer is deposited by the plasma CVD technique on the first layer, the second layer can easily be formed to a desired thickness in a short time.
In accordance with an aspect of the present invention, by forming the first and second layers as insulating, protecting or conductive layers of the same or different types or compositions, the layer member as a insulating, protecting or conductive layer member of desired characteristics can easily be deposited to desired thickness in a short time without inflicting damage on the substrate surface.
In accordance with another aspect of the present invention, by forming the first and second layers as semiconductive layers of the same type or composition, the layer member as a semiconductor layer member can easily be deposited to a desired thickness in a short time without inflicting damage to the substrate surface.
In accordance with another aspect of the present invention, by forming the first and second layers as semiconductor layers of different types or compositions, the layer member can easily be deposited as a semiconductor layer member composed of a first semiconductor layer which may preferably be relatively thin and a second semiconductor layer which may preferably be relatively thick, in a short time without causing damage to the substrate surface.
In accordance with another aspect of the present invention, by forming the first and second layers as an insulating layers and as a conductive or semiconductor layer, respectively, the layer member as a composite layer member can easily be deposited including a conductive or semiconductor layer formed to a desired thickness on the insulating layer of the least possible thickness, in a short time without impairing the substrate surface.
In accordance with yet another aspect of the present invention, by forming the first and second layers as a conductive or semiconductor layer and as an insulating or protecting layer, respectively, the layer member as a composite layer member can easily be deposited including an insulating or protecting layer formed to a desired thickness on the conductive or semiconductive layer of the least possible thickness, in a short time without impairing the substrate surface.
Other objects, features and advantages of the present invention will become more fully apparent from the following description taken in conjunction with the accompanying drawings.